The present invention relates to an electromagnetic clutch which transmits and cuts off power to a compressor employed in a freezing cycle of a vehicle such as a car or the like, and also a ball bearing for applicable in the above electromagnetic clutch.
In a vehicle such as a car or the like, there is employed an electromagnetic clutch which is used to transmit or cut off rotation drive force generated by a running engine to a compressor provided in a freezing cycle such as an air conditioner (an air conditioning system) or the like.
The electromagnetic clutch comprises a rotary body made of metal used as magnetic material such as iron or the like, a body to be rotated made of metal used as magnetic material such as iron or the like, an electromagnetic coil, a bearing for supporting the rotary body in a freely rotatable manner, and the like; and, the electromagnetic clutch allows the rotary body and the to-be rotated body to attract each other due to the attracting force of an electromagnetic coil, thereby being able to carry out the above-mentioned transmission and cut-off of the rotation drive force.
Japanese Patent Unexamined Publication No. Hei. 8-114241 discloses the rotary body of the above-mentioned electromagnetic clutch. The rotary body is supported by a double row ball bearing in which a plurality of balls are arranged along the axis of the ball bearing serving as a center of rotation. This raises a tendency that the width of the double row ball bearing along the axial direction thereof becomes large and thus the electromagnetic clutch itself becomes large in size. As a result of this, the weight of the electromagnetic clutch is caused to increase, thereby increases the manufacturing cost of the electromagnetic clutch.
Also, in the case when, to support the rotary body in a freely rotatable manner, there is used a single row ball bearing in which a single ball is arranged along the axis of the ball bearing, since the sections of grooves formed in the outer and inner races of the single row ball bearing are each formed in a single arc shape, there arises a tendency that a relative shift (which is hereinafter referred to as an axial shift) between the inner and outer races along the axis of the ball bearing becomes large. In general, with limit of elements such as a voltage capable of generating the attracting force of the electromagnetic clutch and the like taken into account, a clearance between the rotary body and the to-be rotated body of the electromagnetic clutch, preferably, may be relatively small, for example, about 0.5 mm.
Further, if the conventional single row ball bearing is used to support the rotary body of the electromagnetic clutch, because the axial shift of this single row ball bearing is large, even when the electromagnetic coil does not generate an attracting force, there is a possibility that the rotary body and the to-be rotated body can be contacted with each other, so that there is a fear that the rotary body and the to-be rotated body can be damaged due to such mutual contact.